Electric motors are well known in the art and are utilized in a wide range of applications ranging from home appliances to large scale industrial use to transport.
The electric motor has changed little since its inception in the sense that its operation is based upon magnetic interactions, namely the repulsive and attractive nature of magnetic interactions between magnetic bodies. It is the controlled interaction of these magnetic interactions which allows an electric motor to create a rotational motion which can in turn be translated into an increase in kinetic energy of the system's rotor.
What has changed is the materials science of the components of an electric motor. Known in the art are permanent magnets which exhibit ever increasing inherent magnetization levels. Insulation techniques for copper wire and other conductive materials allow for the function of an electric motor over a wide operational range. The development of soft ferromagnetic materials enables the use of materials which have a high permeability but low remanence values coupled with low coercivity characteristics and such materials exhibit a narrow and square hysteresis curve or loop.
The hysteresis loop shows the history dependent nature of a magnetization effect on a magnetic material. For example, if a suitable material, which has no magnetization levels, is saturated for the first time it will retain most or all of its magnetization once the external magnetic field used to achieve this saturation is removed. This is the fundamental difference between a permanent magnetic material and a soft ferromagnetic material in that once a soft ferromagnetic material is removed from its influencing magnetization field its magnetization will drop back to zero.
In the field of electromagnetic systems and research, advances have been made in component and equipment functionality, such as in power supplies, current measurement and differential probes, and materials choice for rotors and optical encoders or similar switching controllers. An important advance is the availability of low friction bearings, typically passive magnetic bearings, which provide for restraint of the spindle and allow its attached rotor to rotate about a defined axis at the lowest possible friction cost.
There are several aspects of classical physics which are relevant to this area of electric motors. Faraday's Law is one of the fundamental laws of electromagnetism. In essence the Law states that the electromotive force generated is proportional to the rate of change of magnetic flux.
Following on from Faraday's Law is Lenz's Law, which states that an induced current is always in such a direction as to oppose the motion or change causing it. This Law links electromagnetism to Newton's Third Law which states that for every action there is an equal but opposite reaction.
The implications of these Laws for electric motors are as follows: Counter electromotive force, or CEMF, is the electromotive force or voltage that will push against the applied current and is only caused by a changing magnetic field. Back electromotive force, or BEMF, is a more specific term to electric motors, and is an induced voltage that occurs where there is relative motion between the armature or rotor of the motor and the system's external magnetic field. CEMF or BEMF negatively affects the efficiency of electric motors known in the art.